1. Field of the Invention
The present invention relates to a rotary type compressing apparatus employed in a refrigerant circuit of a cryogenic refrigerator or air conditioning apparatus.
2. Description of the Prior Art
A cryogenic refrigerant apparatus including a rotary compressor is widely known in the art, for instance, from Japanese patent disclosure No. 60-204986. Referring now to FIG. 1, there is provided a refrigerant circuit employing a rotary compressor as disclosed in the above-described Japanese patent disclosure. In the circuit diagram of FIG. 1, a rotary compressor 1 is connected to a condenser 2 which is in turn connected to a control valve 3. The control valve 3 is connected via a capillary tube 4 to an evaporator 5. The evaporator 5 is connected via a check valve 6 to the rotary compressor 1. As is known in the art, these members are connected by refrigerant circuits in series flow relation with the above-defined order. Accordingly, a refrigerant gas is circulated as indicated by arrows, within the closed loop of the cryogenic refrigerant circuit for performing heat exchange.
To improve the above-described conventional refrigerant circuit, another rotary refrigerant compressor, as shown in FIG. 2, is proposed in the above patent disclosure. Referring to FIG. 2, a closed case 7 encompasses a compression element 8, an electrically-powered drive element 9, an jetting pipe 10, and a control valve 3. This compressor is positioned in a refrigerant circuit similar to FIG. 1 for heat exchange.
In the refrigerant circuit as illustrated in FIG. 1, the control valve 3 is controlled in such a way that it is opened during the operation of the compressor 1, whereas it is closed after the compressor 1 is stopped, thereby enabling the refrigerant circuit to be opened and closed. As a result, the control valve 3 can prevent the high-pressure refrigerant located in the condenser 2 and the closed case 7 of the compressor 1 from flowing into the evaporator 5 at a low-pressure and a low temperature through the capillary tube 4 after the compressor 1 is stopped. Since the temperature increases in the evaporator 5 due to the flow of the refrigerant therein is suppressed, the duty cycle of the compressor 1 can be maintained low so that the efficiency of the refrigerant circuit is increased. The function of the check valve 6 is as follows. As the refrigerant flows in the normal direction during the operation of the compressor 1, this valve is opened, whereas it is closed by a pressure difference between the evaporator 5 and the closed case 7 of the compressor 1 after the latter is stopped. Accordingly, this check valve 6 can block the refrigerant at the high-pressure and high temperature conditions that tends to flow into the evaporator 5. FIG. 2 shows a rotary refrigerant compressor in which similar valve controlling is effected by a check valve 6 and a control valve 3 provided. That is to say, during the operation of the compressor 1, the exhaust gas fed into a muffler from the compressor mechanism is exhausted via the jetting pipe 10 into the closed case 7. In this case, as previously described, the control valve 3 mounted on the tip of the jetting pipe 00 is opened and closed by a pressure difference between the exhaust gas in the jetting pipe 10 and the gas in the closed case 7. Simultaneously, this control valve 3 is adapted to open and close a communication hole 12 between the closed case 7 and an exhaust pipe 11, so that the gas present in the closed case 7 is supplied via the exhaust pipe 11 to the refrigerant circuit. Since the above-described pressure difference is no longer present after the compressor 1 has been interrupted, the control valve 3 is closed, whereby the communication hole 12 between the exhaust pipe 11 and the closed case 7 is in the closed condition. As a result, the flow of the high-pressure refrigerant present in the closed case 7 into the evaporator 5 is blocked.
On the other hand, the check valve 6 located in the inhaling path has a substantially same check-valve mechanism as the check valve shown in FIG. 1, and is mounted in the closed case 7. The function of the check valve 6 is to prevent the high-pressure refrigerant in the closed case 7 from flowing into the evaporator 5 via the inhaling path when the compressor 1 is stopped, which is similar to the function of the check valve shown in FIG. 1.
With the above-described construction, the conventional rotary compressor has, however, several drawbacks. Since the high-pressure and high-temperature gas exhausted from the compressor into the muffler 13 is once released via the jetting pipe 10 into the closed case 7, the heat radiation from the exhausted gas may be induced in the closed case 7. Such heat radiation causes the overall temperature of the compressor to considerably increase, resulting in a lower working efficiency of the compressor.
The present invention is made in consideration of the above-described problems in the conventional rotary compressing apparatus.
An object of the invention is to provide a rotary compressing apparatus wherein after the rotary compressing apparatus is stopped, a lower efficiency of the refrigerant unit, or refrigerant circuit due to equilibrium in the pressure of the refrigerant can be avoided.
Another object of the present invention is to provide a rotary compressing apparatus wherein a working efficiency thereof can also be prevented from decreasing by blocking the heat radiation from the exhausted gas.
Still another object of the present invention is to provide a low-cost rotary compressing apparatus.